Conventionally, an image forming apparatus is known in which a light beam emitted by a light source is reflected by a rotating member and is emitted to a photosensitive member. This image forming apparatus has a rotation controller, a forced signal output circuit, a light receiver, and an image data output circuit. The rotation controller controls rotation of the rotating member. The forced signal output circuit outputs a forced lighting signal. The light beam emitted from the light source based on the forced lighting signal and reflected by the rotating member is received by a light receiver. The light receiver outputs a detection signal in response to reception of the light beam. The image data output circuit outputs an image data signal at timing corresponding to output of the detection signal from the light receiver. The light beam emitted from the light source based on the image data signal and reflected by the reflector forms a scanning line on the photosensitive member.
In such an image forming apparatus, the rotation controller and the forced signal output circuit are arranged in the same unit, and are provided at the same integrated circuit chip constituting the unit. A detection signal from the light receiver is inputted to this integrated circuit chip. The rotation controller and the forced signal output circuit are controlled to perform operations based on the detection signal. Further, the rotation controller is connected to the forced signal output circuit, so as to enable communication of signals needed for controlling the operations.